1. Field of Invention
This invention relates to a corrosion inhibitor for sodium chloride brines, and in particular to a corrosion inhibitor which can be used to prevent corrosion of motor vehicles and steel reinforcing members and structures by brines formed by roadway deicing salt.
2. Brief Statement of the Prior Art
Sodium chloride is a widely used industrial chemical. Perhaps the most commonly observed application of sodium chloride is the use of the salt as a road cover in freezing climates, where its high solubility depresses the freezing point of water, thereby melting ice and snow on the surfaces to which it is applied.
A common problem experienced in the various applications of sodium chloride is that the salt promotes corrosive attack on metal surfaces. The corrosiveness of sodium chloride brines is particularly troublesome in the road cover applications where the brine which is splashed on the undersurfaces of cars can cause rapid corrosion and deterioration of the under panels and rocker panels of a car. Since modern car manufacturing techniques have almost universally adopted unitized construction for weight and manufacturing efficiencies, any corrosive attack of brines on the undersurfaces of automobiles is particularly troublesome as the deterioration of such surfaces by corrosion is often not economically repairable. Furthermore, salts added to roads adversely affect roadside vegetation and have been observed to kill roadside trees. These salts are frequently transported as saturated brine solutions in pipelines, and their corrosiveness to steel presents a significant problem to such handling.
The problem of accelerated corrosion by sodium chloride brines is thus a problem which has not, heretofore, been adequately addressed by the prior art. Some solutions to the problem have included the substitution of other salts such as calcium or magnesium acetates or chromates for the road cover applications. These substitutions are not satisfactory because of a prohibitively high cost and because of potentially adverse effects on the environment.
Ideally, any corrosion inhibitor used with sodium chloride should be effective at extremely low concentrations to minimize environmental problems and should be colorless to avoid staining or discoloring of metal surfaces, wearing apparel and the like which come in contact with brine solutions of sodium chloride. The inhibitor should be effective over a very wide range of concentrations, particularly when applied for inhibiting corrosion of brines used in road covers since the brines which are formed by melting of ice and snow in the presence of sodium chloride can be expected to have an extremely wide range of concentration of the sodium chloride. The inhibitor should also be soluble over the wide range of concentrations anticipated in its application. Finally, the inhibitor should be compatible with the sodium chloride manufacturing process and permit the manufacture of granular and corrosion inhibited sodium chloride without any significant effect on the granulation process.